GB2153532A - Producing sound waves in water - Google Patents

Abstract

A water gun type device for producing sound waves in water comprises a cylindrical body 1 having openings 6 at one of its ends, inside which may slide a first mobile assembly formed from a main piston 7 and an auxiliary piston 8 joined together by a rod 9 and a second mobile assembly formed of a secondary piston 10, an annular piston 12 and a hollow rod 11 in which said auxiliary piston slides. A hydraulic circuit associated with a slide valve distributor (see figs 2,3) controlled by a needle valve and a pneumatic circuit provide, when the device is tripped by means of an electromagnetic valve 36, automatic return of the two mobile assemblies to their cocked position. <IMAGE>

Description

SPECIFICATION Improved device for producing sound waves in water Background of the invention 1. Field of the invention The present invention relates to an improved device for producing sound waves in water.

More particularly, the invention relates to a device for emitting sound pulses by the sudden ejection into the water of a liquid mass.

Such a device may be used for example for carrying out seismic prospection operations at sea during which shocks are generated in the water behind the ship pulling a receiver assembly formed of a great number of sensors such as hydrophones spaced out along a sealed sheath which is usually called seismic streamer and in which the echos from the different subterranean reflecting layers are picked up by the receiver assembly and are recorded and processed so as to obtain a representation of the sub soil.

2. Description of the prior art A device is known for generating sound pulses in water by ejecting a liquid mass accumulated in a chamber inside a hollow body, this chamber being open to the outside environment at one of its ends and defined at its opposite end by a first mobile piston. Ejection is obtained by a sudden movement of a first mobile assembly formed of the the first piston and a second piston to which it is connected by a rod, this first mobile assembly cooperating with a second mobile assembly adapted for sliding inside the body and comprising a tubular rod inside which the second piston of the first mobile assembly may slide.The operating cycle comprises the separate or simultaneous movement of the two mobile assemblies under the action of drive means comprising a hydraulic system and a pneumatic system cooperating with a control element actuated by contact between the two mobile assemblies, and control means external to the device for coordinating the movements of the two mobile assemblies and return thereof, after tripping, to their cocked position.

The control means comprise three coaxial cylinders isolated from each other, inside which three pistons interlocked by the same rod move respectively.

The assembly of the three pistons is movable by the action of a hydraulic system on the piston of the middle cylinder. The movement of the corresponding pistons in the other two cylinders, one containing a liquid, the other being connected to a pneumatic system, allows the two mobile assemblies to be moved and the movement of the main piston to be tripped. Operation of the device requires the use of a four way electromagnetic valve and an external control member adapted for actuating the electromagnetic valve at two successive moments in the cycle so as to move the assembly of the three pistons alternately in one direction and in the opposite direction. Such a device is described in U.S.

Patent 4.303.141.

Summary of the invention With the device of the invention, there is no need for a control member for synchronizing the different operating steps and making the cocking operations, after tripping, automatic.

It comprises a tubular body open to the outside environment at one of its ends, a main piston sliding in the body for ejecting a liquid mass therefrom, the main piston being connected to an auxiliary piston for forming a first mobile assembly, a system for controlling the first mobile assembly formed of a second mobile assembly comprising a secondary piston and an annular piston adapted for sliding in the body and connected together by a hollow rod in which the auxiliary piston may slide, the mobile element being provided with a central opening forming a seatforthe main piston and means for generating fluids at a first pressure and a second pressure higher than the first one, these means cooperating with a clapper valve raised by application of the main piston against said seat, raising of the clapper valve putting the space between the main piston and the annular piston at the same pressure as the outside water.

The device is characterized in that it comprises a distributing valve and ducts for applying to one face of the secondary piston a fluid at high or low pressure depending on the position of a mobile part which is movable inside the distributing valve under the action of two antagonistic pressures, one of them being constant, the other being equal to the variable pressure which reigns in said space between the main piston and the annular piston.

The fluid generating means comprise for example a generator of compressed air at a first pressure and a source of hydraulic fluid at a second pressure, the compressed air generator being permanently in communication with the part of the body situated between the secondary piston and the annular piston and with the inside of the hollow rod which connects them together, whatever the position thereof. The variable pressure reigning in said space is equal, in the rest position of the clapper valve, to the pressure generated by the compressed air generator.

The use of the clapper valve, at the time of contact between the two mobile assemblies for modifying the pressure acting on the mobile part of the distributing valve and thus changing the pressures applied to the secondary piston, and the choice of the cross sections of the different elements subjected to the pressures result in making the cocking cycle completely automatic, the cocking phase beginning as soon as the device is tripped.

Brief description of the drawings Other features and advantages will be clear from reading of the description of a preferred embodiment of the device with reference to the accompanying drawings in which: Figure 1 shows schematically in section the device in its cocked position which is also its rest position; Figure 2 shows schematically the distributing valve (a slide valve distributor) for intermittently applying a hydraulic fluid to the secondary piston; Figure 3 shows a more detailed sectional view of the moving part of the clapper valve; Figure 4 shows a schematical sectional view of the device at the end of the tripping phase in which the first mobile assembly has reached the end of its outward stroke and in which the second mobile assembly is about to join it;; Figure 5 shows a schematical sectional view of the device at a subsequent time when the second mobile assembly has joined the first one at the end of its stroke; and Figure 6 shows a schematical sectional view of the device during the return phase of the two mobile assemblies to their cocked position.

Description of the preferred embodiment The device comprises (Figures 1 to 3 more particularly) an elongate tubular body 1 having two coaxial chambers 2,3 with different cross sections which are joined together by a shoulder 4. The smaller section chamber 2 is open on the side opposite shoulder 4 and communicates with the outside environment through a constricted end part 5 of the body provided with openings 6. It also comprises a first mobile assembly formed by a main piston 7 and an auxiliary piston 8 fixed to both ends of a first rod 9, and a second mobile assembly formed by a secondary piston 10 connected by a second rod 11 to an annular piston 12. The section of the main piston 7 and that of the annular piston 12 are equal to the cross section of chamber 2. Annular seals 13, 14 are disposed on their periphery so as to seal the sliding thereof.The cross section of the secondary piston 10 is adapted to the cross section of chamber 3 of the body. An annular seal 15 is disposed on its periphery so as to seal the sliding thereof in chamber 3. The main piston 7 is joined to rod 9 by a truncated cone shaped part 16. A bore 17 having a cross section adapted to that of the auxiliary piston 8 is formed along the axis of the mobile element and of the second rod 11. It is provided at its inlet with a chamfered part 18 having a shape adapted to the truncated cone shaped part 16 of the main piston 7.

A seal 18a is fixed to the annular piston 12 in the vicinity of the chamfered part so as to isolate, from the inside of rod 11, the space 16 in the body between the first piston 7 and the annular piston 12 when they are in abutment against each other. The area S2 of the main piston subjected to the action of the compressed air, when this latter is in contact with the annular piston 12 and with seal 1 8a, is smaller than the facing surface S1 of the auxiliary piston 8. An annular seal 19 is disposed on the periphery of the auxiliary 8 for sealing the sliding thereof. The length of rod 9 is such that, when the truncated cone shaped part 16 comes into abutment on the chamfer 18, the auxiliary piston is substantial ly at the bottom of the central bore 17.

The secondary piston 10 comprises a tubular extension 20, on the side opposite the annular piston 12. This body 1 is closed at its end opposite the constricted part 5, by a cover 21. An annular seal 61 is disposed about the periphery of the cover. This cover is provided with a central bore having a section adapted to that of the tubular extension 20, at least over a part of its length, this central bore comprising a peripheral groove for a seal 22.

An opening 23 is formed in the annular piston 12 for providing permanent communication between the second chamber 3 and the central bore 17 ofthe second rod 11. Two channels 24,25 are formed in the annular piston 12 from the face 1 2a thereof facing the secondary piston 10 (Figure 3). Channel 24 passes therethrough from one side to the other, the other channel 25 communicates with an inner recess 26 opening into the volume 60, on the opposite side 1 2b of the annular piston, through an orifice 27. In recess 26 may slide a control means formed by a needle valve 28 adapted for isolating channel 25 from orifice 27, in the rest position.The needle passes through the orifice 27 and projects outwardly from face 12b so that, when the annular piston 12 comes into abutment against the main piston, the needle is pushed and valve 28 raised, which establishes communication between channel 25 and the space 60 between the two pistons 7 and 12.

The two channels 24 and 25 communicate, through two pipes 29,30, respectively with two channels 31,32 (Figure 1) passing right through the secondary piston 10 and opening into the tubular extension 20 thereof. Three other channels 33, 34,35 also pass through the secondary piston 10 from one side to the other. On one side, they open into the tubular extension 20 and two of them 33,34 are connected to the two channels of a two way electromagnetic valve 36. On the other side, one of the channels 33 opens into the annular space between the second hollow rod 11 and the outer wall of the body, and the other two 34,35 open inside this second rod into a chamber 59 defined by the secondary piston 10 and the axuiliary piston 8.

Channel 35 is very small, at least over a part of its length.

An opening 36 is formed in the side wall of body 1 at the level of the second chamber 3. A pipe 38 connected to a compressed air generator (not shown), is connected to this opening 37 so as to permanently maintain a high pressure (of the order of 140 bars for example) in the part of chamber 3 between the secondary piston and the annular piston 12.

The annular cover 21 at the end of body 1 comprises a part 39 (the detail of which is shown in figure 2) in which is disposed a control system formed essentially by a slide valve distributor 40.

This distributor comprises (Figure 2) a slide-valve formed of three coaxial pistons 41,42,43 joined together by the same rod 44 and movable in a cavity 45 having three communicating chambers 46a, 46b, 46c. A bore 47 is formed through the wall of cover 21 and causes one of the lateral chambers 46a to communicate with the outside. A pipe 48 is fixed at one end to the orifice of channel 31, at the bottom of the tubular recess 20, and at the other end to the output of bore 47. The lateral chamber 46c at the opposite end of cavity 45 is extended by a tubular recess 49 for guiding rod 44, at one of its ends.

Opening into the two opposite chambers 46a, 46c of the cavity are two bores 50a, 50b to which are connected two pipes 51a, 51b (Figure 1) connected to a hydraulic system of a known type and not shown, which is adapted for supplying them with oil respectively at a high and low pressure (240 bars and 1 barforexample).

A communication channel 52 is formed between the intermediate or middle chamber 46c and the end of chamber 3 of the body, on the side of the secondary piston 10 Opposite the annular piston 12 (chamber 62, cf. Figure 4).

The intermediate piston 42 of the slide valve comprises two opposite truncated cone shaped end parts. Two stops 53, 54 are disposed at the two ends of the middle chamber 46b. Their shape is adapted to that of the truncated cone shaped end parts of piston 42 so that, when this latter is applied successively against stop 53 (first position of the slide valve) and against stop 54 (second position of the slide valve) the middle chamber 46b is isolated from chamber 46a or from chamber 46c. Piston 41 slides in chamber 46a while isolating bores 47 and 50a from each other, whatever the position of the slide valve. Piston 43 slides in chamber 46c. A channel 55 places the bore 50b in communication with chamber 46c between piston 43 and bore 49 extending this chamber.The thickness of piston 43 and the position at which channel 55 emerges are chosen so that, in the second position of the slide valve in which the intermediate piston 42 is applied against stop 54, piston 43 closes off the inlet of channel 55. Another channel 56 causes bore 50a to communicate with the tubular recess 49, whatever the position of the slide valve in its cavity. Aflow adjusting means 57 of a known type is disposed in channel 56 for braking the oil flow. A non return valve 63 is connected in parallel across the flow adjusting means 57.

The electromagnetic valve 36 is controlled from a surface installation by means of a conducting cable 58.

The device operates in the following way: The rest position of the device, which corresponds to its cocked position is the one shown in Figure 1.

The second mobile assembly is in its retracted position in which the secondary piston 10 is substantially in contact with the cover 21 of the body. The first mobile assembly is also in the retracted position. In this position, the main piston 7 is in abutment against the annular piston 12 and the needle valve 28 is raised. Communication between channels 24 and 25 is established through orifice 27 and space 60 in chamber 2, and thus the hydrostatic pressure may be exerted through channels 24, 25 and pipes 29,30 and 48 on the piston 41 in the chamber 46a of distributor 40.

The pressure of the oil which is exerted in the opposite direction on rod 44 in recess 49 at the opposite end of the cavity, is such that the supply valve is held in its first position (the one shown in Figures 1 and 2) and duct 52 is in communication with the low pressure oil of pipe 51b.

The secondary piston 10 is subjected, on the cover 21 side (chamber 62) to a low oil pressure and on the other to compressed air at a high pressure and, consequently, is held in a retracted position. The main piston, because the needle valve is raised, is subjected to the hydrostatic pressure on both its faces, except on its truncated cone shaped part facing the central bore 17 where it is subjected to the compressed air. The auxiliary piston is subjected to the hydrostatic pressure through the channel 35 and to the compressed air on its opposite face. The overall force which is exerted on the first mobile assembly and which is the resultant of the forces applied by the compressed air on the unequal areas S1 and S2, results in maintaining the main piston 7 applied against seal 18a.

- then the tripping electromagnetic valve 36 is opened, which places channels 33 and 34 in communication with each other. The compressed air is thus applied to the face of the auxiliary piston facing cover 21 (chamber 3).

The effect of the new resultant of the forces which are exerted on the first mobile assembly is to move it away from the second one. The main piston 7 moves off its seat 18 and the compressed air can be applied to the whole of its face opposite the annular piston 12. The first mobile assembly is then suddenly propelled towards the end part 5 of the body against which it comes into abutment (figure 4} and drives the volume of water contained in the first chamber 2 out through opening 6. The high speed expulsion of the water generates powerful sound waves in the outside environment.

- As soon as the first mobile assembly begins to move away from the second one, the needle valve 28 is closed again and isolates ducts 24 and 25 from each other. The compressed air is then applied to piston 41 of the slide valve through channels 24 and 31, pipe 48 and orifice 47. The ratio of the respective areas of piston 41 and of rod 44 on the recess 49 side, as well as the ratio of the compressed air and oil pressures exerted in opposite directions on the slide valve are such that this latter moves towards its second position (Figure 4) in which the intermediate piston 42 comes to bear on seat 54, which places channel 52 in communication with bore 50a in which a high oil pressure reigns.

Since this high pressure applied to the face of the secondary piston 10 opposite cover 21 (chamber 62) is greater than the compressed air pressure applied to its opposite face, the second mobile assembly is in its turn propelled towards the end 5 of the body where it joins the first one (Figure 5).

During the whole movement phase of the two mobile assemblies towards end 5, the restriction in channel 35 maintains chamber 59 under an overpressure and avoids any entry of outside water.

- With the two mobile assemblies again drawn close together and with the main piston 7 applied against seal 18a, raising of the needle valve 28 results in putting the space 60 between piston 7 and the annular piston 12 at the hydrostatic pressure as well as channels 24,31 and pipes 29,38. The resultant of the forces due to the application of the hydrostatic pressure to the piston of the slide valve and ofthe high pressure of the oil circuit to the rod in the opposite recess 49, results in bringing the slide valve back to its first position (Figure 6). Its movement is delayed by the flow adjustment means 57 so as to avoid a too sudden decompression of space 62 between piston 10 and collar 21.

- With the return of the slide valve to its first position, space 62 is again in communication with the low pressure oil circuit. Since the secondary piston 10 is exposed on its opposite face to the high pressure of the compressed air, the resultant of the forces applied results in bringing back the second mobile assembly to its retracted position (Figure 6).

Since the resultant force applied to the first mobile assembly when the main piston 7 is in contact with the annular piston 12 tends, as we saw above, to apply the main piston 10 thereagainst, the first mobile assembly follows the second one in its retracted movement as far as their cocked position shown in Figure 1. The device is then ready to be tripped again.

It can be clearly seen that the cycle for cocking the device after it has been tripped, by means of the electromagnetic valve 36, is entirely automatic.

Claims (8)

1. An improved device for producing sound waves in water by the sudden ejection of a liquid mass from a tubular body open to the outside environment at one of its ends, said liquid mass being propelled by the sliding of a main piston which is connected to an auxiliary piston for forming a first mobile assembly, said device comprising a system for controlling the first mobile assembly formed of a second mobile assembly comprising a secondary piston and an annular piston adapted for sliding in the body and joined together by a hollow rod in which said auxiliary piston may slide, said annular piston being provided with a central opening forming a seat for the main piston and means for generating fluids at a first pressure and at a second pressure higher than the first one, said means cooperating with a clapper valve raised by the application of the main piston against its seat, the raising of said clapper valve putting the space between said main piston and said annular piston at the same pressure as the outside water, which device further comprises a distributing valve and ducts for applying, to one face of the secondary piston, a high pressure or low pressure fluid, depending on the position of a mobile part which is movable inside the distributing valve under the action of two antagonistic pressures, one of them being constant, the other being equal to the variable pressure which reigns in said space between said main piston and said annular piston.

2. The device as claimed in claim 1, in which the fluid generating means comprise a generator of compressed air at a first pressure and a hydraulic fluid source at a second pressure, wherein said compressed air generator is in permanent communication with the part of the body situated between said secondary piston and said annular piston and with the inside of the hollow rod which connects them together, whatever the position thereof and said variable pressure reigning in said space is equal, in the rest position of the clapper valve, to the pressure generated by said compressed air generator.

3. The device as claimed in claim 2, wherein the mobile part of said distributing valve comprises a central piston, said distributing valve comprises three coaxial chambers, the intermediate chamber communicating with one or other of the two lateral chambers depending on the position ofthe central piston movable in the intermediate chamber, and two lateral chambers communicating respectively with the lower pressure circuit and the high pressure circuit of said hydraulic fluid source, the opposite ends of said mobile part have unequal cross sections, the end having the largest cross section being exposed to the variable pressure and the other being exposed to the high hydraulic pressure and the ratio of the cross sections of the two opposite ends being chosen so that the mobile part moves, when said variable pressure is that of the compressed air, to a position in which said intermediate chamber communicates with the high pressure circuit of said hydraulic fluid source;

4. The device as claimed in claim 3, wherein said central piston is connected by a rod, on the one hand, to a piston sliding in one of the lateral chambers and exposed to the variable pressure and, on the other, to a piston sliding in the other lateral chamber, this latter piston being extended by a rod sliding in a tubular recess which communicates with said high pressure circuit of said hydraulic fluid source.

5. The device as claimed in claim 4, wherein said tubular recess communicates with said high pressure circuit through a channel having a flow regulating means comprising in parallel a circuit element with a non return valve.

6. The device as claimed in claim 4, wherein said space is connected to one end of the cavity of said distributor through channels passing through the annular piston and the secondary piston and associated pipes.

7. The device as claimed in claim 1, wherein the volume of said hollow rod between said auxiliary piston and said secondary piston is in permanent communication with the environment external to the body through a small channel and, intermittently, through a valve with the part of the body in which the first fluid pressure regins permanently.

8. A device for producing sound waves in water as claimed in Claim land as substantially as hereinbefore described with reference to the accompanying drawings.